Filter for humidity control, typically for control of humidity in a bulk liquid tank

ABSTRACT

A filter is includes a housing and at least first and second adsorbent materials within the housing. The second adsorbent material has different characteristic from the first adsorbent material and is in series with the first adsorbent material. When assembled, a labyrinth arrangement is located between a first port in the housing and the first adsorbent material such that gas travels between the first port and the first adsorbent material by passing through the labyrinth arrangement. A filtration system and methods for humidity control of a liquid tank head space uses a filter, including first and second adsorbent and a diffusion channel or labyrinth arrangement

This application is being filed on 5 Mar. 2013, as a PCT Internationalpatent application and claims priority to U.S. Provisional ApplicationSer. No. 61/607,234, filed Mar. 6, 2012, the subject matter of which isincorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to a breather, referred to herein as a “breatherfilter” for controlling the humidity of the air that needs to beexchanged between the environment and the head space inside of a fluidcontainer for a moisture sensitive application, such as a fluid tank, ahydraulic liquid tank, a liquid fuel tank, or an electronic devicecontainer. In particular, this disclosure concerns a breather filterhaving one or more adsorbents to improve adsorbent performance and/orincluding a diffusion channel to slow or eliminate saturation of theadsorbent during no-flow conditions.

BACKGROUND

Breather filters enable the ingression and egression of gas intoreservoirs of oils, hydraulic fluids, and fuels when the fluid level ofthe reservoir changes. It is desirable to remove moisture from the airthat is being drawn into the reservoir, such that the oil or hydraulicfluid is protected from moisture. During egression of the gas from thereservoir, it is desirable to filter that air from contaminants so thatthe ambient air surrounding the reservoir is not polluted.

Prior systems have used breather filters having a single adsorbent bed,which become quickly saturated with water when exposed to humidenvironments, even with no flow. Improvements are desirable.

SUMMARY

In one aspect, a breather filter is provided which includes a housingand at least first and second adsorbent materials within the housing. Inthis disclosure, the terms “breather filter” and “filter” are used. Insome applications the breather filter or filter is configured to removesolid particles in addition to removing moisture. In other applications,the breather filter or filter is not configured to remove solidparticles. The second adsorbent material is different in at least onerespect from the first adsorbent material and is typically in serieswith the first adsorbent material. A labyrinth arrangement is in thehousing and is located between a first port in the housing and the firstadsorbent material such that gas travels between the first port and thefirst adsorbent material by passing through the labyrinth arrangement.

In another aspect, a filtration system for humidity control of a liquidtank head space is provided. The system includes a fluid tank configuredto hold a liquid, such as an oil or hydraulic fluid therein, and a headspace between the liquid and a wall of the tank. A filter, ascharacterized above, is in fluid communication with the head space ofthe tank. When the liquid in the fluid tank drops, air is drawn into thebreather filter through the labyrinth arrangement, the first adsorbentmaterial, the second adsorbent material, and then out of the breatherfilter into the head space of the fluid tank. When liquid in the tankrises, air is forced from the head space, into the filter, through thesecond adsorbent material, then the first adsorbent material, then thelabyrinth arrangement, and then exits the filter to the atmosphere.

In another aspect, a method for controlling humidity of a tank headspace, for example, a liquid tank head space is provided. The methodincludes providing a fluid tank having a liquid therein and a head spacebetween the liquid and a wall of the tank, and a filter in fluidcommunication with the head space of the tank. When liquid in the fluidtank drops, there is a step of drawing gas into the filter from theatmosphere and through a labyrinth arrangement, then through one or moreadsorbent materials in series, and then from the breather filter andinto the head space of the fluid tank. When liquid in the tank rises,there is a step of directing gas from the head space and into thebreather filter, through the one or more adsorbent materials in series(in the reverse direction), then through the labyrinth arrangement, andthen out of the breather filter to the atmosphere.

One embodiment disclosed herein includes a filter for use with a fluidcontainer. The filter includes a housing having a first port and asecond port; at least a first adsorbent material within the housing; andat least a second adsorbent material within the housing layered inseries with the first adsorbent material. The second adsorbent materialtypically has a characteristic different from the first adsorbentmaterial. The first adsorbent material and the second adsorbent materialis arranged within the housing so that gas travels between the firstport and second port by passing through each of the first adsorbentmaterial and the second adsorbent material.

The above-noted second adsorbent material characteristic typically is atleast one of particle size, adsorbent capacity, and/or specific surfacearea.

In one example of the above-noted embodiment, the first adsorbentmaterial adsorbs a greater amount of moisture at a higher relativehumidity than the second adsorbent material.

In another example of the above-noted embodiment, the second adsorbentmaterial changes in color in response to a predetermined level ofadsorption.

In another example of the above-noted embodiment, the first adsorbentmaterial comprises a layer of activated carbon or a blend thereof. Thesecond adsorbent material comprises a layer of silica gel or a blendthereof including calcium sulfate and zeolites.

In preferred embodiments, the labyrinth arrangement acts as a bufferbetween the adsorbent material(s) and the environment around thebreather filter. In other words, the adsorbent inside the breatherfilter is not directly exposed to the environment at large. Instead, airtraveling to the adsorbent travels through the labyrinth and airtraveling from the adsorbent travels through the labyrinth. Thus, whenthe flow of air traveling from the adsorbent stops, the adsorbentremains in contact with a relatively static volume of air that typicallycontains less moisture than the air in the general environment aroundthe breather filter. By keeping the adsorbent in contact with therelatively dry volume, the overall moisture load on the adsorbentdecreases, and the life of the adsorbent increases.

In existing breather filters, if the breather filter and tank is locatedin a humid environment, the breather filter can still be exposed tomoisture from the atmosphere even if the filter is not breathing. Bydiffusion alone, the adsorbent can be exposed to the humid external airconditions. In such conditions, the adsorbent material can quickly reachits capacity of adsorption, even though the equipment that is drawing onfluid in the tank is not being used.

To address this situation, it was recognized that by having a breatherfilter that includes a diffusion channel between the atmosphere and theadsorbent material, any moist air that is drawn in during no-flowconditions, will need to first travel through the diffusion channelbefore reaching the adsorbent material. The diffusion channel introducesa labyrinth or a tortuous path, which serves to restrict and dissipateto preclude entry of moisture and other contaminants into the adsorbentmaterial. This is preferably accomplished without unreasonablypressurizing the reservoir, nor placing it under a substantial vacuum.

Additionally, by using a plurality of specialized adsorbents (adsorbentswith different adsorbing abilities) in combination with the labyrinth orby themselves, it is possible to extend the life and performance of abreather filter. For example, it is possible to provide a synergisticeffect by providing adsorbents in series with each other, an outermostadsorbent having a first adsorbing ability, and a next outermostadsorbent having a second adsorbing ability, and so on. Typically, theoutermost adsorbent material is chosen for optimized performance at highhumidity while the next outermost adsorbent is chosen for optimizedperformance at relatively lower humidity. Thus, the adsorbents work inconcert to progressively dry the air entering the breather.

It is noted that not all of the specific features described herein needto be incorporated in an arrangement for the arrangement to have someselected advantage according to the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, cross-sectional view of a breather filterconstructed in accordance with principles of this disclosure mounted ona fluid tank and illustrating airflow when the fluid level in the tankis dropping;

FIG. 2 is a schematic cross-sectional view of the breather filter andtank of FIG. 1 illustrating airflow when the fluid level in the tank isrising;

FIG. 3 is a top, perspective view of an end cap of a housing of thebreather filter of FIGS. 1 and 2;

FIG. 4 is a bottom perspective view of the end cap of FIG. 3;

FIG. 5 is a top view of the end cap of FIG. 4;

FIG. 6 is a cross-sectional view of the end cap of FIGS. 3-5, thecross-section being taken along the line 6-6 of FIG. 5;

FIG. 7 is an end view of the end cap of FIGS. 3-5;

FIG. 8 is a perspective view of a bottom end cap of the housing of thebreather filter of FIGS. 1 and 2;

FIG. 9 is another perspective view of the end cap of FIG. 8;

FIG. 10 is a top view of the end cap of FIG. 9;

FIG. 11 is a cross-sectional view of the end cap of FIGS. 8-10, thecross-section being taken along the line 11-11 of FIG. 10;

FIG. 12 is a top, perspective view of an alternative embodiment of anend cap of a housing of the breather filter of FIGS. 1 and 2;

FIG. 13 is a top, perspective view of an alternative embodiment of anend cap of a housing of the breather filter of FIGS. 1 and 2;

FIG. 14 is a top, perspective view of an alternative embodiment of anend cap of a housing of the breather filter of FIGS. 1 and 2;

FIG. 15 is a schematic, side view of the example filter cartridgeconstructed in accordance with principles of this disclosure;

FIG. 16 is a schematic cross-sectional view depicting a portion of thefilter cartridge of FIG. 15 and a first end cap of the breather filterof FIG. 1;

FIG. 17 is a schematic, cross-sectional view showing the end cap andfilter cartridge of FIG. 16 operably engaged and connected to eachother;

FIG. 18 is an end view of the inside surface of the end cap of FIG. 16;

FIG. 19 is an end view of the filter cartridge of FIG. 15; and

FIG. 20 is a cross-sectional view, similar to the view of FIG. 16, butshowing an alternate embodiment of an end cap and filter cartridgeportion.

DETAILED DESCRIPTION Overview of Operation, FIGS. 1 and 2

An overview of the operation of one example filter is described inreference to FIGS. 1 and 2. In FIGS. 1 and 2, one example embodiment ofa filter constructed in accordance with principles of this disclosure isshown at 20. The filter 20, shown herein as a breather filter 20, istypically removably attachable to a moisture sensitive container 22,such as a fluid tank 22, holding a reservoir of liquid or fluid 24. Thefluid 24 can be liquid such as hydraulic fluid, oil, fuel, etc, which isintended to be protected from exposure moisture. Together, the breatherfilter 20 and tank 22 form a filtration system 26 used for humiditycontrol of the head space 28 between the fluid 24 and a wall 30 of thetank 22.

The tank 22 generally functions as a storage tank for the fluid 24, suchas hydraulic fluid or oil, that is used with hydraulic equipment (notshown) connected to the tank 22 by way of a fluid port 32. As thehydraulic equipment operates, the fluid level in the tank 22 rises andfalls as the fluid 24 enters and exits the tank 22 by way of the port32. The head space 28 contained between the fluid 24 and the wall 30varies in volume as the level of the fluid 24 fluctuates.

In operation, as the fluid level falls from level A to level B as shownin FIG. 1, the head space 28 expands, drawing in a gas, such as ambientair, from the atmosphere, through a port 48, through breather filter 20,and then into the tank 22. The breather filter 20 removes moisture andparticulate from the incoming air.

In FIG. 2, when the fluid level rises from level B to level A, as shownin FIG. 2, the head space 28 contracts. This contraction forces effluentgas or air out of the tank 22 and through the breather filter 20, andthrough port 48 ultimately out into the atmosphere. In some cases, theeffluent gas can include mist formed from the fluid 24, thus enabling aportion of the fluid 24 to escape from the tank 22. In some embodiments,the breather filter 20 can remove fluid mist from the effluent gas, andin preferred arrangements, the fluid drains back into the tank 22 fromthe breather filter 20.

When the system 26 is in a static state, and the hydraulic equipment isnot operating causing the level of fluid 24 in the tank 22 to change, ifthe atmosphere is of a higher pressure than the pressure in the headspace 28 of the tank, such as in high humid conditions in theatmosphere, ambient air may still be drawn into the breather filter 20even though the hydraulic equipment is not operating. Diffusion may alsobe an issue. The air drawn in or entering via diffusion will typicallyfirst travel through a diffusion channel 34 in the breather filter 20.This diffusion channel will help to prevent the moist ambient air fromreaching the adsorbent materials within the breather filter 20, therebylengthening the life of the breather filter 20.

Example Embodiment of Breather Filter, FIGS. 1-14

In reference first to FIGS. 1 and 2, the breather filter 20 includes ahousing 40. The housing 40 includes an outer surrounding wall 42defining an interior volume 44. The interior volume 44 is for holding atleast one, and preferably a plurality of adsorbent materials 46therewithin. Such adsorbent materials include, for example, activatedcarbon or zeolite. These materials may be arranged in series, in anyorder. In at least one embodiment, however, the selected order is for amaterial that has a higher adsorptive capacity at relatively highhumidity to be located closer to the first port than is another materialwith adsorptive capacity that is greater at relative low humidity.

The housing 40 includes a first port 48 constructed and arranged to bein communication with the atmosphere 50. The first port 48 can be anyarrangement that allows for gas flow or airflow communication betweenthe atmosphere 50 and the internal volume 44 of the housing 40. (As usedherein, the terms “air flow” and “air” are intended to encompass “gasflow” and “gas”, and these terms are used interchangeably throughout andare intended to mean the same thing.) In the embodiment shown in FIGS. 3and 7, the first port 48 includes at least one, and as shown, threeapertures 52 penetrating the wall 42 of the housing 40.

The housing 40 further includes a second port 54. The second port 54 isconstructed and arranged to be in communication with the tank 22. Inparticular, the second port 54 is in airflow of fluid communication withthe head space 28 of the tank 22. In the embodiment illustrated, thefirst port 48 and the second port 54 are at opposite ends of the housing40. In other arrangements, the location of the ports relative to eachother in the housing could be different. Each of the first port 48 andthe second port 54 allows for fluid flow both into the housing 40 aswell as out of the housing 40, depending on which direction the breatherfilter 20 is breathing; that is, whether the breather filter 20 isallowing for ingress or egress of gas relative to the tank 22.

While a variety of constructions for the housing 40 of the breatherfilter 20 are possible, in this particular embodiment, the housingincludes a first end cap 56. The first end cap 56 is removablyattachable to housing body 58. The housing body 58 is defined by theouter wall 42. The first end cap 56 includes an outer surrounding wall60 and an end wall 62. Along an inner surface 64 of the wall 60 arethreads 66 used for removable attachment with a suitably threadedportion 68 along the outer wall 42 of the housing body 58. While theconnection between the first end cap 56 and the housing body 58 is shownas threaded, other ways of attaching these two pieces could be used,such as with a fastener, clamp, interference fit, adhesive, or bracket.In addition, rather than having internal threads on the first end cap 56and external threads on the housing body 58, the reverse could be usedas well.

In this embodiment, the first end cap 56 defines the first port 48.

In the embodiment shown, between the first end cap 56 and the housingbody 58 is a seal member 70. The seal member 70 is for forming a sealbetween the first end cap 56 and the housing body 58 so that any air orfluid that enters or exits the interior volume 44 of the housing 40 mustpass through the first port 48 of the first end cap 56. In theembodiment shown, the seal member 70 is an O-ring 72.

As mentioned previously, the breather filter 20 includes diffusionchannel 34. In this embodiment, the diffusion channel 34 includes alabyrinth arrangement 74 in the housing 40 and in airflow communicationwith the first port 48. By the term “labyrinth arrangement”, it is meantstructure in the housing 40 that forms a deliberately meandering airflowpath that is non-linear (as a whole) and is maze-like. In preferredarrangements, the labyrinth arrangement includes a long path length in arelatively small space. The labyrinth arrangement 74 can be a windingairflow path between the first port 48 and a labyrinth aperture 76providing communication between the labyrinth arrangement 74 and theinterior volume 44 of the housing 40. In the embodiment shown in FIGS. 1and 2, there is a plate 78 between and against the first end cap 56 andthe upper opening 79 formed by the outer wall 42 of the housing body 58.The plate 78 defines the labyrinth aperture 76, and in this embodiment,the labyrinth aperture 76 is a single, circular aperture centered withinthe plate 78. In other arrangements, the labyrinth aperture 76 can be aplurality of apertures in different locations and with differentgeometries. Some of these different geometries include rectangular,rhombus, or square-shaped, pie-wedge shaped, triangular, regular orirregular polygon-shaped, as well as 3-dimensional.

In the embodiment depicted in FIG. 1, the plate 78 is located on thehousing 40, and the majority of the labyrinth arrangement 74 is locatedon the first endcap 56 (with the plate 78 forming one wall of thelabyrinth arrangement 74. However, in some embodiments, the entirelabyrinth arrangement 74 is located completely within the first endcap56. In some embodiments, the entire labyrinth arrangement 74 is locatedwithin the housing 40. In other arrangements, the majority of thelabyrinth arrangement 74 is located on the housing 40, and the firstendcap 56 provides a closing wall for the labyrinth arrangement 74. Insuch an arrangement, the roles of the first endcap 56 and the housing 40with respect to the labyrinth arrangement 74 are reversed compared tothe arrangement described in FIG. 1.

The labyrinth arrangement 74 can be a variety of geometricconfigurations. In reference now to FIGS. 4-6, the labyrinth arrangement74 comprises a labyrinth wall 80 that is part of the first end cap 56and forms a path, preferably a tortuous path 82 between the first port48 and an end location 84, which is in airflow communication with thelabyrinth aperture 76 (FIGS. 1 and 2). In the embodiment shown, the endlocation 84 is centered within the first end cap 56, but it should beunderstood that the end location 84 can be in other locations or in aplurality of locations. In the particular embodiment illustrated inFIGS. 4 and 5, the labyrinth wall 80 forms a spiral channel 86 betweenthe first port 48 and the end location 84. Air that travels between thefirst port 48 and the end location 84 will be forced to travel withinthe airflow path 82 between the labyrinth wall 80 and through the spiralchannel 86. This labyrinth arrangement 74 creates a longer flowpath, ascompared to a system without a labyrinth arrangement 74, thereby slowingdown the rate which moisture in the airflow reaches the adsorbentmaterial 46 in the interior volume 44 of the filter 20. Under staticconditions when the fluid 24 in the tank 22 is not being utilized byequipment, but there are humid conditions that are causing airflow to bedrawn into the breather filter 20, the labyrinth arrangement 74 willslow down the rate which the moisture reaches the adsorbent material 46,and the labyrinth arrangement 74 will resist the diffusion of humid airas the humid air attempts to reach the adsorbent material 46. This willtypically increase the life of the adsorbent material 46 relative to afilter that does not have a labyrinth arrangement.

In preferred arrangements, the labyrinth arrangement 74 will have:

-   -   an L/D ratio of at least 50, in which L is a length of the        spiral channel 86;    -   D is an equivalent channel diameter and is calculated by taking        the square root of (4/pi X A); and    -   A=channel width X the channel height.

It has been found that the L/D ratio is preferably no greater than 380and preferably the L/D ratio should be at about 150, assuming a maximumflow of 100 lpm (3.5 cfm) and a max pressure drop of 0.5 psid. The L/Dratio in these ranges will allow for the life of the adsorbent material46 to be increased sufficiently without an excessive increase in therestriction of airflow between the headspace the atmosphere.

FIGS. 12-14 show embodiments of first end cap 56′ including differentembodiments of labyrinth arrangement 74. In FIG. 12, the labyrintharrangement 74′ includes several parallel channels connected together bycurved ends in a switchback arrangement 200. The switchback arrangement200 can also include one or more sections that are angled relative tothe other sections, such as FIG. 13 (one quartile 202 is angled, in thiscase orthogonally) to the remaining section of the end cap 56. In FIG.14, the labyrinth arrangement 74″ includes are four quartiles 205, 206,207, 208, each angled relative to the next adjacent quartile. In FIG.12, there is a first port 48′ on opposite sides of the end cap 56′,while in FIG. 13, there is only the single location of first port 48′.In FIG. 14, there are 4 first ports 48′ along the outer perimeter of thefirst end cap 56, evenly spaced, about every 90 degrees, each one beingin communication with one of the quartiles 205-208. In each of FIGS.12-14, the labyrinth arrangement 74′, 74″ is in communication with endlocation 84′, which is in airflow communication with the labyrinthaperture 76.

Now in reference to FIGS. 8-11, in this embodiment, the housing 40further includes a second end cap 90. The second end cap 90 is typicallyremovably attachable to the housing body 58 and at an end of the housingbody 58 opposite from where the first end cap 56 is attached. The secondend cap 90 is removably attachable to the housing body 58 throughthreads 92 along an inner surface 94 of a surrounding wall 96. Thesecond end cap 90, in this embodiment, defines the second port 54. Insome embodiments, no second end cap 90 is used, and the housing 40 iscoupled directly to the tank 22.

In preferred arrangements, the second end cap 90 is constructed andarranged to help direct liquid flow into the tank 22. In the embodimentshown in FIG. 11, a funnel surface 98 is formed by having a sloped wall100 directed between the surrounding wall 96 and a neck 102 surroundingand defining the second port 54.

Optionally, as can be seen in FIGS. 9 and 10, the second end cap 90includes a plurality of ribs 104 projecting or extending from the funnelsurface 98. The ribs 104 extend radially between the second port 54 andthe surrounding wall 96. The ribs 104 help to form channels therebetweento direct coalesced liquid into the tank 22. Of course, a variety ofimplementations are possible.

As can be seen in FIGS. 1 and 2, there is a seal member 106 between thesecond end cap 90 and the housing body 58. The seal member 106 forms aseal 108 between the inner surface 94 of the second end cap 90 and theouter wall 42 of the housing body 58, when the second end cap 90 isthreaded in connection to the housing body 58. In the embodiment shown,the seal member 106 is an O-ring 110. Other arrangements and sealmembers can be used.

In reference again to FIGS. 1 and 2, the breather filter 20 includes aplurality of adsorbent materials 46, including at least a firstadsorbent material 120 and at least a second adsorbent material 122within the housing 40. The second adsorbent material 122 is “different”from the first adsorbent material 120 and is layered adjacent to thefirst adsorbent material 120. By “different”, it is meant that theadsorptive material have different specific surface areas, chemicalformulae, sizes, densities, packabilities (how well the particles fittogether), and/or abilities to adsorb moisture. Thus, in someembodiments, the first adsorptive material has a different chemicalcomposition from the second adsorptive material. In other embodiments,particles of first adsorptive material have an average specific surfacearea different from the average specific surface area of particles ofthe second adsorptive material. The first adsorbent material 120 and thesecond adsorbent material 122 are frequently arranged within the housing40 so that fluid or air travels between the first port 48 and secondport 54 by passing through each of the first adsorbent material 120 andsecond adsorbent material 122. In addition, in preferred arrangements,the first adsorbent material 120 is arranged relative to the labyrintharrangement 74 such that fluid or air cannot travel between the firstport 48 and the first adsorbent material 120 without passing through thelabyrinth arrangement 74.

In the arrangement illustrated in FIGS. 1 and 2, the first adsorbentmaterial 120 is between the labyrinth arrangement 74 and the secondadsorbent material 122. As can be seen in the FIGS., the secondadsorbent material 122, in the particular embodiment shown, is betweenthe first adsorbent material 120 and the second port 54.

In preferred arrangements, the adsorbent material that is more closelylocated to the first port 48 has a higher capacity of adsorption at ahigh relative humidity than the other adsorbent material. In thisarrangement, it is the first adsorbent material 120 that has a highercapacity of adsorption than the second adsorbent material 122. In thistype of arrangement, the first adsorbent material 120 has a “betterperformance” at higher levels of humidity than the second adsorbentmaterial 122, which performs better at lower humidity. By “betterperformance”, it is meant that the first material 120 will adsorb agreater amount of moisture at a higher relative humidity than the secondmaterial 122 will adsorb; and, the second material 122 will adsorb agreater amount of moisture at a lower relative humidity than the firstmaterial 120 will adsorb. The first adsorbent material 120 has acapacity of adsorption tuned to higher relative humidities than thesecond adsorbent material 122. Stated another way, the first adsorbentmaterial 120 and the second adsorbent material have different “moisturesorption isotherms”. In this context, “moisture sorption isotherms”refers to the water vapor capacity of a sorbent (activated carbon,zeolite, etc.) at various water vapor concentrations (percent relativehumidity). The measurements were performed at one temperature(isothermal) and plotted as capacity (percent weight) vs. water vaporconcentration (percent relative humidity “rh”).

While in the embodiment shown, there are two different layers ofadsorbent material 120, 122, it should be understood that in embodimentsusing the diffusion channel 34, a sole or single layer could be used;alternatively, more than two layers of other adsorbent materials or thesame materials but arranged layered with different ones in between,could be used. In embodiments that do not use the diffusion channel 34,at least two or more different layers of adsorbent material 120, 122 areused. When at least two layers of adsorbent material 120, 122 are used,there is synergy between the layers. For example, the first layer 120 isadapted to adsorb a greater amount of moisture at a higher relativehumidity than the second layer 122 will adsorb; and, the second layer122 is adapted to adsorb a greater amount of moisture at a lowerrelative humidity than the first layer 120 will adsorb. Accordingly, forexample, a 2 inch depth comprising the first and second layers 120, 122as described herein will remove more moisture than a 2 inch depth ofeither of the first layer 120 or the second layer 122 alone wouldremove.

In one embodiment, the first adsorbent material 120 comprises activatedcarbon or a blend thereof. The second adsorbent material 122 maycomprise a silica gel material and is a material that changes in colorin response to a predetermined level of adsorption. When the secondadsorbent material 122 changes color, this can provide a visualindication to a user that the breather filter 20 needs to be serviced orreplaced. The housing 40, in this example, can be partially or entirelytransparent. For example, the housing 40 may comprise transparent PVC orpolycarbonate.

In one example embodiment, the second adsorbent material 122 comprisessilica gel or a blend thereof. Instead of silica gel or mixed withsilica gel there can include calcium sulfate and/or zeolites.

In the embodiment shown, the breather filter 20 includes no more thanthe first adsorbent material 120 and the second adsorbent material 122.In one example, the first adsorbent material 122 consists essentially ofan activated carbon or consists essentially of a layer of activatedcarbon and a color changing agent. In one example, the second adsorbentmaterial 122 consists essentially of silica gel or consists essentiallyof silica gel and a color changing agent. An example of a color changingagent includes cobalt chloride used in DelSORB AB25B® from DELTAADSORBENTS.

In review of FIGS. 1 and 2, it should be appreciated that the labyrinthaperture 76 in the plate 78 is in fluid communication with the firstadsorbent material 120.

A variety of implementations are possible. In the particular embodimentshown in FIGS. 1 and 2, the first adsorbent material 120 and the secondadsorbent material 122 are separated by a porous scrim 124, which couldalso be a porous plate, or a porous plate layered with one or morescrims. The scrim 124 typically separates the layers of adsorbents, andthe plates provide structural support to the scrim 124. The scrim 124 orplate may have O-ring seal members 126, 128 to help seal and hold thescrim 124 or plate in place within the housing 40.

In this particular arrangement, between the second adsorbent material122 and the second port 54 is expansion foam 130. The foam 130 helps toprevent the adsorbent materials 120, 122 from movement within thehousing 40, and it also helps to contain the adsorbent material 46within the housing 40. Between the second adsorbent material 122 and thefoam 130 is a plate or scrim 132 that is shown in this embodiment asbeing held in place with first and second O-rings 134, 136 along the topand bottom of the plate or scrim 132. The scrim 132 can also function asa filter.

In FIG. 1, grooves 138, 139 can be seen along the inner surface 43 ofthe housing 40. These grooves 138, 139 allow for alternate locations forholding 0-rings and plates or scrim, to allow for flexibility of howmuch and what proportion of first adsorbent material 120 and secondadsorbent material 122 to utilize.

In FIG. 1, it should be noted that the first adsorbent material 120,second adsorbent material 122, and the foam 130 are shown schematically,with only a portion being illustrated. It should be realized that thesematerials would occupy the entire volume in the indicated space withinthe interior volume 44 of the housing 40. That is, in the embodiment ofFIG. 1, the first adsorbent material 120 occupies the entire volumebetween the plate 78 and the scrim or plate 124. The second adsorbentmaterial 122 occupies the entire volume between the scrim or plate 124and the plate or scrim 132. In a preferred arrangement, air or fluidtypically does not have a path between the first port 48 and second port54 without passing through both the first adsorbent material 120 andsecond adsorbent material 122. In a preferred arrangement, air or fluidtypically flows between the first port 48 and second port 54 by passingthrough both the first adsorbent material 120 and second adsorbentmaterial 122.

In some preferred systems, the upper bound for the pressure differentialcaused by flow through the labyrinth arrangement 74 will be not greaterthan 0.5 psid for both ingression and egression. Preferably, in idealconditions, the breather filter 20 will operate below 0.5 psi, whichequates to about 13.8 inches of water, and more preferably, less than 7inches of water of pressure differential. In one embodiment, the path ofthe spiral channel 86 will have a channel width of 8 mm, with a depth of5 mm and a length of about 128 cm. In this type of geometry, thepressure differential will be 0.164 inches of water at 0.5 lpm. In oneexample, assuming the maximum flow of 100 lpm (3.5 cfm) and maximumpressure differential of 0.5 psid, then the minimum L/D ratio of 50includes a relative humidity (RH) rising to 50% of final in 160 hours.An L/D ratio of about 150 has an RH rising to 50% of final in 500 hours.A maximum L/D ratio of 380 has the pressure differential at its limit,and the RH rises to 50% of final in greater than 1,000 hours.

In other words, in typical environments for this application, theoutside atmosphere 50 has a higher relative humidity than the protectedenclosure in the interior 44 of the breather filter 20. Over time, themoisture from the outside atmosphere 50 diffuses into the interiorvolume 44 of the filter 20, and the humidity within the filter 20increases until relative humidity between the interior volume 44 andoutside atmosphere 50 are equal. The longer and narrower the channel 86is (resulting in a higher L/D ratio), the longer this equalizationtakes, which lengthens the life of the filter 20. The penalty for alarge L/D ratio is a high pressure drop when air is forced through thechannel. A lower pressure drop is desirable, in many situations, so inmany applications, a workable solution is balance the desirablequalities of having a lengthened life of the adsorbent 46 by having alarge L/D ratio, while without causing too much pressure drop when flowis required by having a small L/D. As summarized above, preferablesolutions include having an L/D ratio of at least 50, no greater than380, and preferably at about 150.

Example Methods

The above construction or variations of it can be used in a method forcontrolling humidity of a liquid tank headspace. For example, theheadspace 28 of the tank 22, or container, can have its humiditycontrolled by breather filter 20. The method includes providing thefluid tank 22 having a liquid 24, such as hydraulic fluid or oil,therein and headspace 28 between the fluid 22 and wall 30 of the tank22. The breather filter 20 is in fluid communication with the headspace28 of the tank 22. The method includes when liquid 24 in the tank 22drops, drawing air into the breather filter 20 and through the labyrintharrangement 74, then through the first adsorbent material 120, thenthrough the second adsorbent material 122, and then from the breatherfilter 20 and into the headspace 28 of the tank 22. The labyrintharrangement 74 helps to coalesce any moisture in the atmosphere 50before it reaches the first adsorbent material 120. The labyrintharrangement 74 creates a long diffusion path length, acting as a barrierto any moisture reaching the first adsorbent material 120 underquiescent conditions. Air that does reach the first adsorbent material120 and second adsorbent material 122 has any further moisture adsorbedby the adsorbent materials 120, 122.

The method also includes, when the liquid 24 in the tank 22 rises,directing the liquid from the headspace 28 and into the breather filter20. The liquid 24 in the headspace 28 can be air, gas, or a mist. Fromthe headspace 28, the air, gas, or mist is directed through the secondadsorbent material 122, then through the first adsorbent material 120,then through the labyrinth arrangement 74, and then out of the breatherfilter 20 to the atmosphere 50. In some arrangements, before beingdirected through the second adsorbent material 122, the fluid may bedirected through foam 130, which helps to coalesce any oil mist intodroplets that is then drained out of the breather filter 20 through thesecond port 54.

The step of drawing air into the breather filter 20 includes drawing theair through the labyrinth arrangement 74, which includes a wall in thefirst end cap 56 of the housing 40 for the breather filter 20, and inexample embodiments, the wall 80 of the labyrinth arrangement 74 formsspiral channel 86.

In one example embodiment, the color of the second adsorbent material122 is monitored, and when it changes color, the breather filter 20 isserviced. The breather filter 20 may be serviced by removing it from thetank 22 and replacing it with a new breather filter. In someembodiments, the breather filter 120 is serviced by removing it from thetank and then detaching the end caps 56, 90 from the housing body 58 andreplacing the internal adsorbent material 46 and foam 130. The firstadsorbent material 120 and second adsorbent material 122 may be replacedwith new, fresh adsorbent material, or it may be recharged by drawingand removing the moisture.

In one method of use, if the fluid 24 in the tank 22 is not beingutilized by equipment, there still may be a draw of air from theatmosphere 50 into the breather filter 20 due to humid conditions. Inthis method, the air is drawn in through the first port 48 and thenalong the path 82 created by the labyrinth wall 80. This path 82 willslow down the rate that moisture reaches the first adsorbent material120, as compared to a breather filter that it did not have the labyrintharrangement 74 between the first port 48 and the first adsorbentmaterial 120.

Experimental

Testing was done in two phases. Initial work was performed on the VTIVapor Sorption Analyzer (‘VTI’) with later work taking place on a custombuilt breakthrough test bench.

Analysis & Discussion

Isotherms

WV-B1500, an activated carbon from MeadWestVaco, had the highestcapacity, absorbing almost 130% of its own weight in water, with half ofthe capacity existing at higher than 70%. However, the material hasnearly no performance at the low end of the humidity scale.

Silica gel offers reasonable performance at the low and medium humidityranges, but lacks capacity at the high end. The silica gel testedmanaged to reach 35 wt % pickup as a maximum. It should also be notedthat the silica gel reaches half its maximum capacity at the value of35% rh.

Zeolite 4A reaches half capacity at 5% rh. Reaching half capacity atsuch a low humidity level means that it offers only minimal capacityincreases at humidity levels greater than 20% rh.

Briefly summarized:

Regular Liquid Tight Liquid Req Req Loose Liq Req Low Air All zeolitebased All silica gel based Any sorbent Humidity sorbent sorbent package(<20% rh) Mild Air Zeolite and silica Activated carbon All silica gelHumidity gel sorbent and silica gel based sorbent (20-60% rh) sorbentHigh Air Active system Activated carbon Activated Humidity required andsilica gel sorbent carbon and (>60% rh) silica gel sorbent

Alternate Embodiments, FIGS. 15-20

In FIG. 15, a filter cartridge 220 is schematically illustrated incross-section. The filter cartridge 220 can be used in a filterassembly, such as the assembly shown by breather filter 20.

The filter cartridge 20 is removable and replaceable in the breatherfilter assembly 20. For example, the cartridge 220 can be mountedbetween the first end cap 56 and the second end cap 90.

The cartridge 220 includes a cartridge shell 222 and a top cover 224. Inone example embodiment, the shell 22 and cover 24 are molded from thesame construction, and are a single piece of molded material. In otherembodiments, the shell 22 and cover 24 may be separate pieces ofmaterial and fixed together.

The shell 222 defines a cartridge interior 226. The cartridge interior226 includes at least first adsorbent material 120 and at least secondadsorbent 122. The second adsorbent 122 is layered in series with thefirst adsorbent 120. The second adsorbent 122 has a characteristicdifferent from the first adsorbent 120, as previously discussed inconnection with the earlier embodiments.

The top cover 24 includes a gas opening 228. The gas opening 228 isdefined by a boundary 230. In the example shown in FIG. 15, the gasopening 228 is centered on the top cover 224. In other embodiments, thegas opening 228 can be in locations different than the center of the topcover 224. The boundary 230 can be a penetrable boundary 230.

The first adsorbent material 120 and the second adsorbent material 122are arranged within the cartridge interior 226 so that gas travelsthrough the cartridge 220 by passing through the gas opening 228 andthen through each of the first adsorbent material 120 and secondadsorbent material 122.

In the example embodiment shown in FIG. 15, the cartridge 220 can alsoinclude a foam layer 130, as described in connection with the previousembodiments.

Still in reference to FIG. 15, in the embodiment shown, a penetrablefilm 232 is shown covering the gas opening 228. This film 232 is tocontain the contents of the cartridge interior 226, when the cartridge220 is not in use installed on a filter assembly. The film 232 willprevent, for example, the first adsorbent material 120 from spilling outthrough the gas opening 228.

The film 232 is penetrable in that, when installed in use in a filterassembly, the user can easily remove the film 232 to expose the gasopening 228. In addition, this removal of the film 232 can be donethrough engagement with the first end cap 234 (FIG. 16), to be discussedfurther below.

In reference now to FIG. 19, in cross-section viewed in a directionperpendicular to a direction in which the first and second adsorbentmaterials 120, 122 are arranged, along the gas opening boundary 230 ofthe top cover 224 is a plurality of alternating recesses 236 andsegments 238. A variety of shapes can be used. In the embodimentillustrated, the alternating segments 238 are arched segments 240. Therecesses 236 are illustrated as being generally triangle shaped 242.

As with the previous embodiments, the second adsorbent material 122 hasa characteristic different from the first adsorbent material 120. Thischaracteristic can include at least one of particle size, adsorbentcapacity, and/or specific surface area. Further, as with the previousembodiments, the first adsorbent material 120 adsorbs a greater amountof moisture at a higher relative humidity than the second adsorbentmaterial 122.

As with the previous embodiments, the second adsorbent material 122 canchange in color in response to a predetermined level of adsorption. Itcan be helpful to have the shell 222 be made from a clear or transparentmaterial so that color change can be visually detected.

In reference now to FIGS. 16-18, the first end cap 234 is illustrated.The first end cap 234 is analogous to the first end cap 56, describedpreviously, and which description is incorporated herein by reference.One difference between the end cap 56 and the end cap 234 is that thereis no threaded connection for the end cap 234. Rather, the end cap 234removably attaches to the filter cartridge 220. There are many ways toremovably attach the filter cartridge 220 to the end cap 234. In theexample shown, there is a snap fit connection 246 (FIG. 17) between anaperture border 260 in the end cap 234 and the gas opening 228 of thecartridge 220.

In the example shown in FIG. 16, the first end cap 234 includes an outerwall 250 defining a first port 252. The first end cap 234 also includesan end wall 254.

As with the previous embodiments, the first end cap 234, in thisembodiment, includes labyrinth arrangement 74. The labyrinth arrangement74 is within the outer wall 250 and is closed on one side by the endwall 254. As with the previous embodiment, the labyrinth arrangement 74is structure that forms an air flow path that is non-linear andmaze-like. The labyrinth arrangement 74 includes labyrinth wall 80 thatforms tortuous path 82 between the port 252 and an aperture 258.

The aperture 258 has a border 260 defined by a labyrinth wall 262. Theaperture border 260 has a height that is greater than a height of thelabyrinth arrangement 74.

In the example embodiment shown, the aperture border 260 includes aplurality of spaced projections 264. Spaced between the projections 264are segments 266, and in the example shown, the segments 266 are archedshaped.

The tortuous path 82, formed by the labyrinth arrangement 74 forms a gasflow channel 268 flowing between the labyrinth wall 262. From a reviewof FIG. 16, it can be seen how the channel 268 is closed by the closedtop end wall 254 of the first end cap 234, while it has an open side 263opposite of the closed top end 254. The open side 263 of the channel 268will be closed when the end cap 234 is operably connected to thecartridge 220.

The first end cap 234 includes a bottom end 270 that is open and incommunication with the channel 268 formed by the labyrinth arrangement74. The open bottom end 270 can receive the cartridge 220 there within.

As with the previous embodiments, the labyrinth wall 262 can be in theshape of a spiral channel 86 between the port 252 and the aperture 258.Certain preferred relationships between the length of the spiral channel86 and the equivalent channel diameter may be as previouslycharacterized, in which a ratio of L/D is at least 50, and A is equal tothe channel width taken times the channel height, and the equivalentchannel diameter D is equal to the square root of (4/pi X A). In someembodiments, the L/D ratio is no greater than 380. In some embodiments,the L/D ratio is about 150.

FIG. 16 illustrates the first end cap 234 and the filter cartridge 220before they are releasably attached together. FIG. 17 illustrates thefirst end cap 234 and the filter cartridge 220 connected together. InFIG. 17, it can be seen how the aperture border 260 including theprojections 264 snap within the gas opening 228 of the top cover 224 ofthe cartridge 220 to form snap connection 246.

In the example shown, the projections 264 are received within therecesses 236 of the gas opening 228, while the arched segments 266 areadjacent to the arched segments 240 of the gas opening 228.

The projections 264 can include a deflectable lip 272 that deflects andsnaps in engagement with the gas opening boundary 230 of the cartridge220. This snap engagement will releasably connect to the first end cap234 to the cartridge 220.

After the first end cap 234 is attached to the cartridge 220, theexterior surface 225 of the top cover 224 closes the open side 263 ofthe labyrinth 74. In this way, the air that enters the port 252 flowsthrough the channel 268, which is closed on the upper end by end wall254, and at the open side 263 by the exterior surface 225 of the topcover 224.

One example air flow path is shown in FIG. 17. Gas can be seen enteringthe port 252 at arrow 274. The gas then flows through the labyrintharrangement 74 by flowing within the channel 268 and through thetortuous path 82. The gas then emerges from the channel 268 of thelabyrinth arrangement 74 through the aperture 258. The gas then flowsthrough the aperture 258 and into the cartridge 220 through the gasopening 228, which is releasably attached to the first end cap 234. Fromthere, the gas flows through the first adsorbent 120 and secondadsorbent 122.

FIG. 20 illustrates an alternate embodiment of the cartridge,illustrated at 220′ and of the first end cap, illustrated at 234′. Inthis embodiment, the filter cartridge 220′ includes labyrintharrangement 74 connected to the top cover 224′. For example, thelabyrinth arrangement 74 can be molded as the same piece as the topcover 224′. Alternatively, the labyrinth arrangement 74 can bemechanically fixed to the top cover 224 of the cartridge 220′. Otherthan the location of the labyrinth arrangement 74, the cartridge 220′ isthe same as the cartridge 220 of FIG. 15.

The first end cap 234′ is the same as the first end cap 234, with theexception that there is no labyrinth arrangement 74 in the first end cap234′.

In use, the first end cap 234′ is mounted over the cartridge 220′. Thereis engagement between the boundary 230 of the gas opening 228 in thecartridge 220′ and the aperture border 260 of the first end cap 234′.When the first end cap 234 is operably mounted onto the cartridge 220′,the inner wall surface 278 of the end wall 254 closes the top openchannel 268 of the labyrinth 74. This then results in the gas flowflowing through the port 252 at arrow 274 and then through tortuous path82 created by the labyrinth 74 that is closed on the top by the innerwall surface 278 of the end wall 254 and at the bottom by the top cover224′. The gas exits the labyrinth 74 at the aperture 258 and then flowsinto the cartridge 220 through the gas opening 228, and then through thefirst and second adsorbent materials 120, 122.

The above represents principles and examples. Many arrangements arepossible.

1. A filter for use with a moisture sensitive container; the filtercomprising: (a) a housing assembly having a first port and a secondport; (b) at least a first adsorbent material within the housing; (c) atleast a second adsorbent material within the housing assembly andlayered in series with the first adsorbent material; the secondadsorbent material having a characteristic different from the firstadsorbent material; (i) the first adsorbent material and the secondadsorbent material arranged within the housing assembly so that gastravels between the first port and second port by passing through eachof the first adsorbent material and the second adsorbent material; and(d) a labyrinth arrangement in fluid communication with the first portand being between the first port and the first adsorbent material; thelabyrinth arrangement being located such that gas travels between thefirst port and the first adsorbent material by flowing through thelabyrinth arrangement.
 2. A filter according to claim 1 wherein: (a) thefirst adsorbent material is between the labyrinth arrangement and thesecond adsorbent material; (b) the second adsorbent material is betweenthe first adsorbent material and the second port; and (c) the firstadsorbent material adsorbs a greater amount of moisture at a firstrelative humidity than the second adsorbent material adsorbs at thefirst relative humidity.
 3. A filter according to claim 2 wherein: (a)the second adsorbent material adsorbs a greater amount of moisture at asecond relative humidity than the first adsorbent material adsorbs atthe second relative humidity.
 4. A filter according to claim 3 wherein:(a) the second adsorbent material changes in color in response to apredetermined level of adsorption. 5.-9. (canceled)
 10. A filteraccording to claim 1 wherein: (a) the labyrinth arrangement forms achannel between the first port and an aperture; and (b) an L/D ratio isat least 50, wherein L is a length of the channel and D is an equivalentchannel diameter, in which: A=channel width X channel height; andD=square root of (4/pi X A). 11.-12. (canceled)
 13. A filtration systemfor humidity control of a fluid tank headspace comprising: (a) a fluidtank configured to hold a liquid therein and a headspace between theliquid and a surface of the tank; and (b) a filter in fluidcommunication with the headspace of the tank; the filter including (i) ahousing assembly having a first port in communication with atmosphere;and a second port in communication with the headspace of the fluid tank;(ii) at least a first adsorbent material within the housing assembly;(iii) at least a second adsorbent material within the housing assemblyand layered in series with the first adsorbent material; the secondadsorbent material having a characteristic different from the firstadsorbent material; (A) the first adsorbent material and the secondadsorbent material arranged within the housing assembly so that gastravels between the first port and second port by passing through eachof the first adsorbent material and the second adsorbent material; and(iv) a labyrinth arrangement in fluid communication with the first portand being between the first port and the first adsorbent material; thelabyrinth arrangement being located such that gas travels between thefirst port and the first adsorbent material by passing through thelabyrinth arrangement; wherein, when liquid in the fluid tank drops, gasis drawn in through the first port, the labyrinth arrangement, the firstadsorbent material, the second adsorbent material, and then through thesecond port to flow into the headspace of the fluid tank; and, whenliquid in the tank rises, air is forced from the headspace, through thesecond port, the second adsorbent material, the first adsorbentmaterial, the labyrinth arrangement, and then exits through the firstport to the atmosphere. 14.-20. (canceled)
 21. A filter cartridge foruse in a filter assembly; the filter cartridge comprising: (a) acartridge shell including a surrounding wall and a top cover; the shelldefining a cartridge interior; (i) the top cover having a gas openingcovered with a penetrable boundary; (b) at least a first adsorbentmaterial within the cartridge interior; (c) at least a second adsorbentmaterial within the cartridge interior and layered in series with thefirst adsorbent material; the second adsorbent material having acharacteristic different from the first adsorbent material; and (i) thefirst adsorbent material and the second adsorbent material arrangedwithin the cartridge interior so that gas travels through the cartridgeby passing through each of the first adsorbent material and the secondadsorbent material.
 22. A filter cartridge according to claim 21 whereinthe penetrable boundary includes a penetrable film covering the gasopening.
 23. A filter cartridge according to claim 21 wherein: (a) thetop cover, in cross-section viewed in a direction perpendicular to adirection in which the first and second adsorbent materials arearranged, includes a plurality of alternating recesses and segmentsalong the gas opening boundary.
 24. A filter cartridge according toclaim 23 wherein: (a) the alternating segments are configured to matewith a detachable end piece.
 25. A filter cartridge according to claim23 wherein: (a) the second adsorbent material characteristic includes atleast one of particle size, adsorbent capacity, and/or specific surfacearea.
 26. A filter cartridge according to claim 21 wherein: (a) thefirst adsorbent material adsorbs a greater amount of moisture at ahigher relative humidity than the second adsorbent material.
 27. Afilter cartridge according to claim 21 wherein: (a) the second adsorbentmaterial changes in color in response to a predetermined level ofadsorption.
 28. A filter cartridge according to claim 21 furthercomprising: (a) a labyrinth arrangement secured to the top cover; thelabyrinth arrangement forming a channel in communication with and endingat the gas opening.
 29. A filter cartridge according to claim 28wherein: (a) the labyrinth arrangement comprises a wall forming a spiralchannel ending at the gas opening.
 30. An end cap for use with a filterassembly; the end cap comprising: (a) an outer wall defining a firstport; (b) a labyrinth arrangement within the outer wall; the labyrintharrangement forming a channel between the first port and an aperture;(i) the aperture having a border defined by a labyrinth wall; theaperture border having a height greater than a height of the labyrintharrangement; the aperture border including a plurality of spacedprojections; (c) a closed top end; and (d) an open bottom end incommunication with the channel formed by the labyrinth arrangement. 31.An end cap according to claim 30 wherein: (a) the labyrinth arrangementcomprises a wall in the end cap forming a tortuous path between thefirst port to the aperture; and (b) the wall in the first end cap formsa spiral channel between the first port and the aperture.
 32. An end capaccording to claim 30 wherein: (a) an L/D ratio is at least 50, whereinL is a length of the channel and D is an equivalent channel diameter, inwhich: A=channel width X channel height; and D=square root of (4/pi XA).
 33. An end cap according to claim 32 wherein: (a) the L/D ratio isno greater than
 380. 34. An end cap according to claim 32 wherein: (a)the L/D ratio is about
 150. 35. (canceled)